Illegal or not?

[zokemon]

How are you using them? Like on your server?
If you are using images from another server on your own, that is the illegal part to begin with. Go to the server that has the image you want and ask them if you can use their tree graphic. Then you can go rename it to what ever you want. I find almost all classic managers to be rather stingy with their files though as if Graal was a competition to get the best server. Go figure!